How much power?

I am planning to crossfire my 7950 with a 7970. I will be running them both at 1070/1500 clocks, and I also have my x6 phenom II overclocked too 4.0ghz. My current PSU is a 750w PCP&C MKII Silencer, and it is silver rated. I'm just wondering if my PSU will handle all the overclocks. I'm pretty sure it will but barely. I also have 7x120mm fans and 6 hard drives if that even matters much. One last thing that I read was that this unit can actually supply a fair amount over 750w. Somewhere around 820w and higher.

I also have a thermaltake toughpower 750w that is 7 years old, but it hasn't been used in two years. If that one would be a better option then I can always swap them out.

Any insight would be appreciated, and if need be I can remove some stuff to free up power.

Here is my PSU: http://www.guru3d.com/articles_pages/pc_power_and_cooling_silencer_mkii_750w_psu_review,8.html